Placoderm Eyes

Placoderm eyes are evolutionary intermediates claims an ANU press release, 12 December 2008, and an article in ScienceDaily 2 January 2008. Gavin Young of the Australian National University has studied the eye structure of a fossil placdoerm, an extinct fish that had bony plates embedded in its skin. The fossil was found in limestone around Lake Burrinjuck in New South Wales dated as being 400 million years old. The soft tissue of the fish’s eye is not preserved but placoderm eye sockets are lined with a layer of thin bone which shows where the nerve canals and muscle attachments were. Young described his findings as follows: “Part of the trouble in tracing the evolution of the eye is that soft tissues don’t tend to fossilise. But the eye cavities in the braincase of these 400 million-year-old fossil fish were lined with a delicate layer of very thin bone. All the details of the nerve canals and muscle insertions inside the eye socket are preserved – the first definite fossil evidence demonstrating an intermediate stage in the evolution of our most complex sensory organ. These extinct placoderms had the eyeball still connected to the braincase by cartilage, as in modern sharks, and a primitive eye muscle arrangement as in living jawless fish.” He went on to say: “What this research shows is that 400 million years ago there was already a complex eye, and one that was an intermediate form between jawless and jawed vertebrates.” This means that we’re able to add one more piece to the puzzle of how the human eye came to be.”

Editorial Comment: If “400 million years ago there was already a complex eye”, then this fossil does not explain how complex eyes came into existence. The evidence actually shows that extinct placoderms had a combination of two functional features that are not seen together in living fish. This does not make it evidence of one changing into the other. That could only be proven by observing such a change, which is impossible because placoderms are extinct. (Ref. vision, ichthyology)